This invention relates to an optical head provided in the head unit of an optical information recording-reproducing apparatus such as a magneto-optical disk apparatus.
Along with the present day development of optoelectronics, there have been manufactured optical information recording-reproducing apparatus capable of recording and/or reproducing and/or erasing audio or image formation at a high performance and at random by the use of a light beam.
For example, in an optical video apparatus, recorded information comprising a projection (pit) pattern on a disk surface formed of transparent acrylic resin, transparent polycarbonate or the like is detected by an optical head and is photoelectrically converted, whereafter it is properly gain-adjusted by an amplifier and is further converted into a predetermined analog amount through a reproducing circuit such as a D-A converter, whereafter it is output by the use of an output device.
Originally, an optical head displays its function as an optical head only by having various optical parts being mounted therein. As shown, for example, in FIG. 1 of the accompanying drawings, a semiconductor laser 1 and a collimator lens (mounted in a collimator lens barrel 2) are adjusted, or as also shown in FIG. 1, polarizing beam splitters (PBS's) 3, 6, 7, an objective lens (mounted in an objective lens barrel 4), a condensing lens barrel 5, a servo sensor 8 for obtaining the focus control signal and/or the tracking control signal of a light beam directed to a recording medium, and an RF sensor (a magneto-optical signal detecting sensor) 9 for obtaining the reproduced signal of information recorded on the recording medium are mounted in the head body.
FIG. 1 is a perspective view showing the arrangement of optical parts in an optical head according to the prior art.
Here, a beam condensed by the condensing lens 5 passes through the polarizing beam splitter 6 and further passes through a toric lens 11 adhesively secured to the polarizing beam splitter 6 and reaches the servo sensor 8. To narrow the pull-in range of the focus and increase the sensitivity of the focus when a focus error signal is obtained by the servo sensor, it is necessary to make the focal length (back focal length) of the condensing lens 5 great and also necessary to bring the radii of the meridional line and latitudinal line of the toric lens 11 close to each other. However, to provide a compact and light-weight optical head, it is necessary to shorten the distance from the condensing lens 5 to the servo sensor 8 and therefore, there has been a construction as shown, for example, in FIG. 1 wherein the toric lens 11 is adhesively secured to the polarizing beam splitter 6.
However, in the so-called separation optical type as shown in FIG. 2 of the accompanying drawings which has a fixed head portion 21 in which a laser 33, etc. are fixed to the apparatus body, if instead of adopting an arrangement similar to the so-called unitary type in which a laser, an objective lens, etc. are made into a unitary construction, an attempt is made to narrow the pull-in range of the focus and thereby increase the focus sensitivity, the distance from the condensing lens 5 to the servo sensor 8 will become long. Particularly, the distance from the toric lens 11 to the servo sensor 8 will also become long, and this will pose a serious problem when making the drive device compact from a full height size to a half height size.
Further, the adjustment of the toric lens 11 to the optic axis is effected through the polarizing beam splitter 6 and therefore, the error is increased, and in the combined use type wherein the sensor 8 obtains a focus error signal and a tracking error signal, this has led to a problem that the leak from the tracking error signal into the focus error signal, i.e., the so-called cross talk amount, becomes great.
The present invention has been made in view of the above-noted problems and an object thereof is to provide an optical head in which it is possible to increase the accuracy of adjustment of a condensing lens barrel and a toric lens on the optic axis and reduce the cross talk amount and to make a drive device compact.
The above object is achieved by the following optical information recording-reproducing apparatus of the present invention.
The optical information recording-reproducing apparatus of the present invention comprises:
a light source unit producing a light beam applied to an optical information recording medium;
first optical means disposed in an optical path leading from said light source unit to the optical information recording medium for directing the light beam from said light source unit to the optical information recording medium and separating the light beam passed through said optical information recording medium from the light beam from said light source unit;
second optical means for condensing the light beam passed through said optical information recording medium and separated by said first optical means, said second optical means comprising a first condensing lens, a holding member for holding said first condensing lens, and a second condensing lens mounted on said holding member;
a first light receiving member for receiving the light beam condensed by said second optical means to obtain the focus control signal and/or the tracking control signal of the light beam directed to the optical information recording medium through said first optical means; and
a second light receiving member for receiving the light beam condensed by said second optical means to obtain the reproduced signal of information recorded on said optical information recording medium.
More particularly, the apparatus of the present invention is characterized in that a toric lens or a cylindrical lens is joined to a condensing lens barrel provided on the optical path of the light beam after being passed through the optical information recording medium, at the emerging position of the light beam passed through said lens barrel.